1. Field of the Invention
The present invention relates to improved Schottky barrier junction devices and methods of fabrication thereof. More particularly, the invention concerns the use of a layer of an intermetallic compound of tantalum, zirconium, hafnium, niobium, titanium or nickel in combination with aluminum upon a semiconductor substrate to form a Schottky barrier contact. The invention also concerns various methods for fabricating such Schottky barrier contacts.
2. Description of the Prior Art
The use of Schottky barrier junctions is well known in the prior art. Thus, a Schottky barrier junction comprises a rectifying metal -- semiconductor junction produced by plating, evaporating or sputtering any of a variety of metals upon N-type or P-type semiconductor materials. The more commonly used metals are the electrode metals such as molybdenum, tungsten and aluminum, or aluminum alloy with copper; and the semiconductor most commonly utilized is silicon. The electrical characteristics of such metal to semiconductor junctions are well known to depend upon the work function of the metal as well as the electron affinity of the semiconductor. Moreover, the energy necessary for an average electron to flow in the reverse direction across the barriers is determined largely by the barrier height of the junction, where the barrier height is found to be equal to the difference in work function between the metal and a semiconductor. From this relationship, it follows that an essential requirement of forming a diode junction is that the work function of the metal must exceed the corresponding property of the semiconductor in order that a barrier be present. If this condition is not met an ohmic contact is formed.
In the case of aluminum, tungsten and molybdenum it has been found that Schottky barrier junctions can be formed utilizing N-type silicon having a doping less than 8 .times. 10.sup.16 atoms/cc. It is also recognized that other metals, such as hafnium can be utilized with P-type silicon having the above mentioned doping levels to form Schottky barrier junctions. With the usual aluminum-silicon barrier, a barrier height in the order of 0.68 - 0.72 electron volts is possible where pure metal exists at the junction after the usual settling operation employed for fabricating the devices.
Schottky barrier junctions fabricated in accordance with the foregoing parameters are suitable for many purposes. However, a need exists in the art for a Schottky barrier junction design and method of fabrication thereof of devices having uniform and temperature stable characteristics. In addition, a need exists for a method of fabricating Schottky barrier junctions which have adjustable and highly predictable barrier heights, that at the same time exhibit good electrical characteristics. Finally, a need exists for a method for fabricating such Schottky barrier junctions which produces devices exhibiting good planarity at the useful silicon interface.
It has been found by the inventors of the present application, that Schottky barrier junctions exhibiting the above mentioned desirable characteristics can be fabricated utilizing several different methods by utilizing intermetallic compounds of a certain group of transition metals with aluminum. The use of intermetallic compounds of some of the transition metals with aluminum is disclosed in pending U.S. Patent Application Ser. No. 625,439, filed Oct. 24, 1975 for "Intermetallic Layers in Thin Films for Improved Electro Migration Resistance" by James K. Howard and Paul S. Ho. The above mentioned application does not disclose the use of intermetallic compounds in connection with Schottky barrier junctions, however.